b = input().split(' ')
n = int(b[0])
k = int(b[1])
a = input().split(' ')
for i in range(len(a)):
    a[i] = int(a[i])
l = list()
for i in range(1,n-1):
    if a[i-1] >= a[i] and a[i+1] >= a[i]:
        #print('first')
        l.append(k - min(a[i-1],a[i+1]) + a[i])
    elif a[i-1] < a[i] and a[i+1] < a[i]:
        #print('second')
        l.append(k - a[i] + max(a[i-1],a[i+1]))
m = min(l)
if(m<=0):
    print(0)
else:
    print(m)